1. Field of the Invention
The present invention relates to an antenna system, and more particularly to an integrated dual-polarized printed monopole antenna for WLAN (wireless local area network) application, providing polarization diversity to combat multipath fading effect in wireless communication system.
2. Description of the Related Art
With the prosperous development in wireless communications, the users also become very demanding in communication quality. It is required that the communication products be thinner, lighter, shorter and smaller, and stable communication quality is also a big concern. However, the multipath fading effect significantly reduces the communication quality of the system. Accordingly, it is necessary to employ antenna diversity to combat the multipath fading effect in wireless communication system.
Generally speaking, conventional antenna diversity can be accomplished in the form of frequency diversity, time diversity, or spatial diversity. In frequency diversity, the system switches between frequencies to combat multipath fading effect. In time diversity systems, the signal is transmitted or received at two different times to combat multipath fading effect. In spatial diversity systems, two or more antennas are placed at physically different locations to combat multipath fading effect.
U.S. Pat. No. 5,990,838, issued to Burns et al. on Nov. 23, 1999 entitled xe2x80x9cDual Orthogonal Monopole Antenna System,xe2x80x9d discloses a spatial diversity antenna system having a pair of monopole antennas respectively disposed on the top and bottom surfaces of the printed circuit board which has a first and a second dielectric layers, a conducting ground plane disposed between the first and second dielectric layers, wherein the pair of antennas are mutually orthogonal, and a feeding circuit is coupled to the pair of antennas for connecting to a principal system.
Although U.S. Pat. No. 5,990,838 has provided an antenna system of spatial diversity to improve the multipath fading effect in wireless communication system, it still fails to obtain optimal reflection coefficient (S11) and isolation (S21) for combating the multipath fading effect. Furthermore, U.S. Pat. No. 5,990,838 needs to use multilayer printed substrate, which requires a complex structure and high fabrication cost.
Therefore, it is necessary to provide an antenna system for effectively solving the problems of conventional art mentioned above, so as to obtain optimal reflection coefficient (S11) and isolation (S21) for combating the multipath fading effect in wireless communication system.
It is a primary object of the present invention to provide an integrated dual-polarized printed monopole antenna having optimal reflection coefficient (S11) and isolation (S21) to combat the multipath fading effect in wireless communication system.
It is another object of the present invention to provide an integrated dual-polarized printed monopole antenna with polarization diversity to combat the multipath fading effect in wireless communication system.
It is a further object of the present invention to provide an integrated dual-polarized printed monopole antenna which has a simple structure and can be fabricated at lower cost.
In order to achieve the above objects, the present invention provides an integrated dual-polarized printed monopole antenna mainly comprising:
a microwave substrate having a first and a second surfaces; a first monopole antenna disposed on the first surface of the substrate and excited by a first 50-xcexa9 microstrip line through a first feeding port; a second monopole antenna disposed on the first surface of the substrate and excited by a second 50-xcexa9 microstrip line through a second feeding port, and the second monopole antenna being mutually perpendicular to the first monopole antenna; and a metallic ground plane disposed on the second surface of the substrate, the metallic ground plane having a main metallic ground plane and a protruded metallic ground plane extending between the first and the second monopole antennas.
According to another aspect of the present invention, the main metallic ground plane is rectangular or substantially rectangular shape, wherein two adjacent corners thereof are respectively cut off a 45xc2x0 edge portion, and the lengths of the two cut edge portions are the same.
According to a further aspect of the present invention, both the first and the second monopole antennas are straight radiating metallic lines of same length, and are resonant at quarter-wavelength, and extend outwardly respectively at 90xc2x0 on the two cut edge portions of the main metallic ground plane.
According to a still further aspect of the present invention, the protruded metallic ground plane is rectangular or substantially rectangular, wherein one side thereof extends from the main metallic ground plane between the two cut edge portions, and the length thereof is about 1.5 times of the first and second monopole antennas, and the width thereof is about 0.8 times of the first and second monopole antennas.
According to the present invention, the protruded metallic ground plane is capable of effectively reducing the coupling between two monopole antennas to obtain better isolation and impedance matching. The experimental results of an antenna design embodiment of the present invention for WLAN application at 2.4-GHz band show that employing the protruded metallic ground plane for the operating frequencies within the WLAN band (2400-2484 MHz) can make the isolation of the two monopole antennas less than xe2x88x9227 dB. In addition, the measured radiation pattern in the embodiment also shows that the antenna has good dual-polarized radiation characteristics. The antenna according to the present invention has a simple structure, small volume, and is very easy to implement, to integrate with related circuits, and suitable for applications in WLAN (wireless local area network) systems.